As is well known in the art, gear systems find numerous applications in transferring the motion of one rotating shaft to another shaft. To prevent damage to the gear teeth contact surfaces, which may be caused by, e.g., excessive friction between meshing teeth while the gears rotate, a lubricant may be applied onto the contact surfaces. Typically, nozzles are arranged to discharge a constant flow of lubricant directly onto the teeth. The prior art shows arrangements where the lubricant strikes the teeth either before, after, or at the point where the teeth of one gear mesh with the teeth of another. See U.S. Pat. Nos. 1,309,113, 2,017,871, 2,302,822, 2,793,714, 2,840,186, 3,075,690, 3,146,629, 3,170,292, and 3,738,452. See also K. Fujita, et al., Journal of Engineering for Industry, Transaction of the ASME, Vol. 98, Series B, No. 2 (May 1976), pp. 635-644; G. van Heijningen, Tribology International, Vol. 17, No. 2 (Feb. 1984), pp. 11-18; and D. Dudley, Handbook of Practical Gear Design, McGraw-Hill, Inc., 1984, pp. 7.45-7.46, TJ184.D784. To maximize the depth that the lubricant is driven between the teeth of the rotating gears, the speed of the lubricant should approximate or exceed the rotational speed of the teeth, U.S. Pat. No. 1,717,814.
In a bevel gear arrangement shown in U.S. Pat. No. 3,788,426, lubricant is sprayed onto the teeth of rotating gears, at the point where the teeth mesh. Due to centrifugal forces, some of the lubricant is thrown off of the teeth. To limit the thrown off lubricant from striking other components within the gearbox, a perforate screen partially surrounds at least one of the gears. As the lubricant is thrown off of the gear surrounded by the screen, the lubricant strikes the screen, and loses most of its kinetic energy. The lubricant then drains into a sump from where it is scavenged and recirculated through the gearbox.
Van Heijningen notes that if the amount of lubricant thrown off of the gear teeth is significant, the mesh point may become starved of lubricant, which could lead to gear failure. However, he points out that operating efficiencies may decrease if the mesh point is flooded with too much lubricant in an attempt to compensate for lubricant throw off. According to R. Drago, Fundamentals of Gear Design, 1982, p. 9.24, if too much lubricant is supplied to the gear system, the lubricant may be violently churned by the gears, which could generate excessive, undesired heat within the gearbox.
Centrifugal forces are used to distribute lubricant throughout a gearbox in U.S. Pat. No. 4,429,587. Lubricant is directed into a hollow shaft of a gear, the shaft having channels which extend radially therethrough. During rotation of the gear, the lubricant moves radially outwardly through the channels due to centrifugal forces, and the channels direct the lubricant onto other gear components within the gearbox.
As the speeds and the load transferring requirements of gear systems increase, the need for more effective lubrication of gear teeth becomes apparent. Also, as operating conditions become more severe, more heat is generated in the gear system, and more effective means for removing the excess heat from the system are required. Accordingly, scientists and engineers are seeking new and improved ways to lubricate and maintain the temperature of gear systems.